Link adaptation using transmission rate options

ABSTRACT

This disclosure provides systems, methods, and apparatus, including computer programs encoded on computer-readable media, for link adaptation in a wireless local area network (WLAN). A link adaptation test packet from a first WLAN device to a second WLAN may include a plurality of link adaptation test portions that are generated using a corresponding plurality of transmission rate options. For example, the plurality of link adaptation test portions may be modulated using different modulation and coding scheme (MCS) options. Thus, a single test packet may be used to evaluate different transmission rate options. The second WLAN device may provide feedback information regarding the link adaptation test portions. The feedback information may be used to determine a transmission rate for a subsequent transmission from the first WLAN device to the second WLAN device based on wireless channel conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application is a Continuation of U.S. patent applicationSer. No. 17/103,550, by YANG et al., entitled “LINK ADAPTATION USINGTRANSMISSION RATE OPTIONS,” filed Nov. 24, 2020, which claims priorityto U.S. Provisional Patent Application No. 62/942,703, by YANG et al.,entitled “LINK ADAPTATION WITH MODULATION AND CODING SCHEME (MCS)SELECTION,” filed Dec. 2, 2019, each of which is assigned to theassignee hereof, and each of which is expressly incorporated byreference herein.

TECHNICAL FIELD

This disclosure relates to the field of wireless communication, and moreparticularly to link adaptation in a wireless local area network (WLAN).

DESCRIPTION OF THE RELATED TECHNOLOGY

A wireless local area network (WLAN) may be formed by one or more accesspoints (APs) that provide a shared wireless communication medium for useby a number of client devices also referred to as stations (STAs). Thebasic building block of a WLAN conforming to the Institute of Electricaland Electronics Engineers (IEEE) 802.11 family of standards is a BasicService Set (BSS), which is managed by an AP and including one or morewirelessly connected STAs associated with the AP. A station (STA) mayhave a wireless connection (referred to as a wireless association, orjust “association”) when it has authenticated and established a wirelesssession with the AP.

Two or more WLAN devices (such as an AP and a STA) may establish acommunication link to communicate with each other via the sharedwireless communication medium. Depending on the conditions on thecommunication link, the WLAN devices may adjust transmission parametersto optimize throughput or reliability of transmissions on thecommunication link. For example, the transmission parameters may beadjusted to account for radio conditions, environmental impediments,pathloss, interference due to signals of other transmitters, sensitivityof the receiver, or transmitter power, among other examples.

SUMMARY

The systems, methods, and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein. The innovative aspects mayinclude any combination of the following implementation options.

One innovative aspect of the subject matter described in this disclosurecan be implemented as a method performed by a first wireless local areanetwork (WLAN) device. The method may include transmitting a firstpacket from a first WLAN device to a second WLAN device via a wirelesschannel. The first packet may include a plurality of link adaptationtest portions generated using a corresponding plurality of transmissionrate options. The method may include receiving, from the second WLANdevice, feedback information based on the plurality of link adaptationtest portions in the first packet. The method may include determining aselected transmission rate option for transmission of a subsequentpacket to the second WLAN device via the wireless channel based on thefeedback information.

In some implementations, the plurality of transmission rate optionsincludes different modulation and coding scheme (MCS) options. In someimplementations, the plurality of link adaptation test portions includesa first portion modulated using a first MCS and a second portionmodulated using a second MCS option.

In some implementations, the first packet has a format based on a nulldata packet (NDP) defined for the WLAN.

In some implementations, the first packet includes an indication tocause the second WLAN device receive to the plurality of link adaptationtest portions using the corresponding plurality of transmission rateoptions and provide the feedback information based on the plurality oflink adaptation test portions.

In some implementations, the first packet is a dedicated link adaptationtest packet having a format specified by a link adaptation protocol.

In some implementations, the first packet includes upper layer data forthe second WLAN device in addition to the plurality of link adaptationtest portions.

In some implementations, the upper layer data is included in a separateportion of the first packet that is different from the plurality of linkadaptation test portions.

In some implementations, the plurality of link adaptation test portionsincludes a first portion that is modulated in a first set of tones of anorthogonal frequency division multiplexed (OFDM) symbol and a secondportion that is modulated in second set of tones of the same OFDMsymbol.

In some implementations, the plurality of link adaptation test portionsincludes a first portion and a second portion of the first packet aremodulated in different orthogonal frequency division multiplexed (OFDM)symbols associated with transmission of the first packet.

In some implementations, the first packet includes a series of OFDMsymbols, each OFDM symbol being modulated using a different transmissionrate option.

In some implementations, the feedback information includes a field thatindicates the selected transmission rate option that was selected by thesecond WLAN device.

In some implementations, the feedback information includes one or morelink quality metrics related to the plurality of link adaptation testportions. The method may include determining, by the first WLAN device,the selected transmission rate option based on the one or more linkquality metrics.

In some implementations, the one or more link quality metrics mayinclude a log-likelihood ratio (LLR), a signal to noise ratio (SNR), asignal to interference plus noise ratio (SINR), an error vectormagnitude (EVM), or any combination thereof.

In some implementations, receiving the feedback information includesreceiving an acknowledgement (ACK) message in response to the firstpacket. The ACK message may include a field populated with the feedbackinformation.

In some implementations, the first packet is a request to send (RTS)packet. In some implementations, receiving the feedback informationincludes receiving a clear to send (CTS) message in response to the RTS.The CTS message may include a field populated with the feedbackinformation.

In some implementations, each of the plurality of link adaptation testportions is modulated using a different modulation and coding scheme(MCS) option. The feedback information may include an LLR metricindicative of a decoding success rate for each of the plurality of linkadaptation test portions. In some implementations, determining theselected transmission rate option may include selecting an MCS optionassociated with a link adaptation test portion having a highestthroughput and for which the corresponding LLR metric is above athreshold.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as a method performed by a second WLANdevice. The method may include receiving, from a first WLAN device via awireless channel, a first packet that includes a plurality of linkadaptation test portions generated using a corresponding plurality oftransmission rate options. The method may include transmitting feedbackinformation to the first WLAN device based on the plurality of linkadaptation test portions in the first packet. The feedback informationmay be usable by the first WLAN device to determine a selectedtransmission rate option for transmission of a subsequent packet fromthe first WLAN device via the wireless channel.

In some implementations, the plurality of transmission rate optionsincludes different MCS options. The plurality of link adaptation testportions may include a first portion modulated using a first MCS and asecond portion modulated using a second MCS option.

In some implementations, the method may include determining one or morefirst link quality metrics based on the first portion of the firstpacket. The method may include determining one or more second linkquality metrics based on the second portion of the first packet.

In some implementations, the method may include determining the feedbackinformation includes the one or more first link quality metrics and theone or more second link quality metrics.

In some implementations, the method may include determining the selectedtransmission rate option based on the plurality of link adaptation testportions in the first packet. The feedback information may include afield that indicates the selected transmission rate option.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as an apparatus of a first WLAN device.The apparatus may include at least one modem configured to output afirst packet for transmission from the first WLAN device to a secondWLAN device via a wireless channel. The first packet may include aplurality of link adaptation test portions generated using acorresponding plurality of transmission rate options. The at least onemodem may be configured to obtain, from the second WLAN device, feedbackinformation based on the plurality of link adaptation test portions inthe first packet. The apparatus may include at least one processorcommunicatively coupled with the at least one modem and configured todetermine a selected transmission rate option for transmission of asubsequent packet to the second WLAN device via the wireless channelbased on the feedback information.

In some implementations, the plurality of transmission rate optionsincludes different MCS options. In some implementations, the pluralityof link adaptation test portions includes a first portion modulatedusing a first MCS and a second portion modulated using a second MCSoption.

In some implementations, the first packet includes an indication tocause the second WLAN device to the plurality of link adaptation testportions using the corresponding plurality of transmission rate optionsand provide the feedback information based on the plurality of linkadaptation test portions.

In some implementations, the first packet is a dedicated link adaptationtest packet having a format specified by a link adaptation protocol.

In some implementations, the first packet includes upper layer data forthe second WLAN device in addition to the plurality of link adaptationtest portions.

In some implementations, the apparatus includes at least one transceivercoupled to the at least one modem and a plurality of antennas coupled tothe at least one transceiver to wirelessly transmit signals output fromthe at least one transceiver. The apparatus may include a housing thatencompasses the at least one modem, the at least one processor, the atleast one transceiver and at least a portion of the plurality ofantennas.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as an apparatus of a second WLAN device.The apparatus may include at least one modem configured to obtain, froma first WLAN device via a wireless channel, a first packet that includesa plurality of link adaptation test portions generated using acorresponding plurality of transmission rate options. The apparatus mayinclude at least one processor communicatively coupled with the at leastone modem and configured to determine feedback information based on theplurality of link adaptation test portions in the first packet, thefeedback information usable by the first WLAN device to determine aselected transmission rate option for transmission of a subsequentpacket from the first WLAN device via the wireless channel. Theapparatus may include the at least one modem configured to output thefeedback information for transmission to the first WLAN device.

In some implementations, the plurality of transmission rate optionsincludes different MCS options. The plurality of link adaptation testportions may include a first portion modulated using a first MCS and asecond portion modulated using a second MCS option.

In some implementations, the apparatus includes at least one transceivercoupled to the at least one modem and a plurality of antennas coupled tothe at least one transceiver to wirelessly transmit signals output fromthe at least one transceiver. The apparatus may include a housing thatencompasses the at least one modem, the at least one processor, the atleast one transceiver and at least a portion of the plurality of Anotherinnovative aspect of the subject matter described in this disclosure canbe implemented as a computer-readable medium having stored thereininstructions which, when executed by a processor, causes the processorto perform any one of the above-mentioned methods.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as a system having means for implementingany one of the above-mentioned methods.

Details of one or more implementations of the subject matter describedin this disclosure are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a pictorial diagram of an example wireless communicationnetwork that supports the use of a link adaptation test packet.

FIG. 2 shows an example link adaptation protocol that uses a linkadaptation test packet.

FIG. 3 shows an example message flow diagram of a link adaptationprotocol using a link adaptation test packet.

FIG. 4 shows an example link adaptation test packet and examplecorresponding modulation and coding scheme (MCS) options.

FIG. 5A depicts a first example feedback message format.

FIG. 5B depicts a second example feedback message format.

FIG. 6A depicts a block diagram of an example transmitting WLAN devicethat supports link adaptation.

FIG. 6B depicts a block diagram of an example receiving WLAN device thatsupports a link adaptation.

FIG. 7 depicts an example link adaptation test packet using timedivision for test portions.

FIG. 8 depicts an example link adaptation test packet in which thetesting signals are included in a padding section of a data carryingpacket.

FIG. 9A shows an example conceptual diagram in which an orthogonalfrequency division multiplexing (OFDM) symbol includes multiple linkadaptation test portions.

FIG. 9B shows an example conceptual diagram in which multiple OFDMsymbols may be used for a link adaptation test packet.

FIG. 9C shows an example conceptual diagram in which the link adaptationtest portions are included in a resource unit of an orthogonal frequencydivision multiple access (OFDMA) transmission.

FIG. 10 shows a flowchart illustrating an example process by atransmitting WLAN device to support link adaptation.

FIG. 11 shows a flowchart illustrating an example process by a receivingWLAN device to support link adaptation.

FIG. 12 shows a block diagram of an example wireless communicationdevice.

FIG. 13A shows a block diagram of an example access point (AP).

FIG. 13B shows a block diagram of an example station (STA).

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following description is directed to some particular implementationsfor the purposes of describing innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein can be applied in a multitude ofdifferent ways. The described implementations can be implemented in anydevice, system or network that is capable of transmitting and receivingradio frequency (RF) signals according to one or more of the Instituteof Electrical and Electronics Engineers (IEEE) 802.11 standards, theIEEE 802.15 standards, the Bluetooth® standards as defined by theBluetooth Special Interest Group (SIG), or the Long Term Evolution(LTE), 3G, 4G or 5G (New Radio (NR)) standards promulgated by the 3rdGeneration Partnership Project (3GPP), among others. The describedimplementations can be implemented in any device, system or network thatis capable of transmitting and receiving RF signals according to one ormore of the following technologies or techniques: code division multipleaccess (CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA(SC-FDMA), single-user (SU) multiple-input multiple-output (MIMO) andmulti-user (MU) MIMO. The described implementations also can beimplemented using other wireless communication protocols or RF signalssuitable for use in one or more of a wireless personal area network(WPAN), a wireless local area network (WLAN), a wireless wide areanetwork (WWAN), or an internet of things (IOT) network.

A WLAN (sometimes also referred to as a Wi-Fi™ network) in a home,apartment, business, or other area may include one or more WLAN devices.An access point (AP) is a WLAN device that includes a distributionsystem access function. The AP may provide distribution system accessfor one or more stations (STAs) that are associated with the AP. An APmay provide a wireless coverage area for devices to access the WLAN viaa wireless channel. STAs can establish a wireless association (alsoreferred to as a wireless link, wireless connection, or the like) viathe channel configuration of an AP to access the WLAN. A transmittingWLAN device (which may be an AP or a STA) may establish a communicationlink with a receiving WLAN device over a wireless channel.

The conditions of the wireless channel may impact a transmission rate orother parameters of the communication link. Link adaptation (sometimesalso referred to as rate adaptation) refers to the determination of thetransmission rate (such as selecting a modulation and coding scheme(MCS)) and other parameters for a communication link based on theconditions of a wireless channel. In some implementations, link adaptionmay include selecting beamforming or a spatial stream configuration fora MIMO transmission. A traditional process for link adaptation requiresa series of packets and packet feedback to converge on an optimaltransmission rate (such as an optimal MCS). For example, thetransmitting WLAN device may use a first selected MCS when sending oneor more first packets. The transmitting WLAN device may select adifferent MCS for later packets based on feedback (such as anacknowledgement or negative acknowledgement) regarding the one or morefirst packets or based on a packet error rate (PER) associated with theone or more first packets. Thus, the traditional process of selecting anoptimal MCS for the communication link may require an inefficient anditerative process over a consecutive series of adjustments. Meanwhile,the channel conditions may change before the WLAN devices converge onthe optimal transmission rate. Furthermore, different manufacturers anddevices may implement different link adaptation procedures. Performanceand channel efficiency may be degraded as a result of traditional ad hocmethods for link adaptation.

This disclosure provides systems, methods, and apparatus, includingcomputer programs encoded on computer-readable media, for linkadaptation in a wireless local area network. The techniques in thisdisclosure may be used in a fast rate adaptation (FRA) protocol forefficiently determining the transmission rate (such as an MCS) and otherparameters for a communication link based on the conditions of awireless channel. Various implementations relate generally todetermining a transmission rate for wireless communications from atransmitting WLAN device to a receiving WLAN device. The transmissionrate may be defined by, among other parameters, an MCS selected based onchannel conditions. A WLAN may support different transmission rateoptions depending on the channel conditions. In accordance with thisdisclosure, the transmitting WLAN device may send a first packet as partof a fast rate adaptation protocol. The first packet also may bereferred to as a link adaptation test packet (or a “test packet” forshort). The test packet may include different portions (also referred toas test portions) associated with different transmission rate options.For example, the test packet may include a first portion modulated usinga first MCS and a second portion modulated using a second MCS. Thesource data encoded in the first portion and the second portion mayinclude testing sequence (such as a predetermined testing sequence) thatenables the receiving WLAN device to determine the fidelity of thetransmission after decoding the first portion using the first MCS anddecoding the second portion using the second MCS. A receiving WLANdevice can observe the various portions of the test packet for thepredetermined testing sequence using the different MCS and providefeedback information indicative of the decoding success rate for eachportion. A transmitting WLAN device may use the feedback information toselect a transmission rate option for a later transmission from thefirst WLAN device to the second WLAN device.

In some implementations, the receiving WLAN device can determine qualitymetrics for the different test portions corresponding to differenttransmission rate options in the test packet. The quality metrics (whichalso may be referred to as link quality metrics or transmission ratequality metrics) may be indicative of the how suitable a transmissionrate option is based on the wireless channel conditions. The qualitymetrics may be based on decoding or signal processing of the varioustest portions of the test packet. For example, the quality metrics mayinclude log-likelihood ratio (LLR), signal to noise ratio (SNR), signalto interference plus noise (SINR), error vector magnitude (EVM), biterror rate (BER), or block error rate (BLER), among other examples. Thereceiving WLAN device may send feedback to the transmitting WLAN devicein response to the test packet so that the transmitting WLAN device canselect an optimal transmission rate for the subsequent transmission. Forexample, the transmitting WLAN device may select a transmission rateoption that corresponds with the test portion having a highest qualitymetric. Alternatively, or additionally, the transmitting WLAN device mayselect a transmission rate option that corresponds with the test portionhaving a highest throughput from among transmission rate options forwhich the quality metric is above a threshold. In some implementations,the feedback may include separate quality metrics for each of themultiple test portions. Alternatively, or additionally, the feedback mayinclude an indication of a transmission rate option (such as an MCSoption) selected by the receiving WLAN device. For example, thereceiving WLAN device may select the optimal MCS based on the qualitymetrics and include an indicator related to the selected MCS in thefeedback to the transmitting WLAN device.

In some implementations, the test packet may include the different testportions in a single orthogonal frequency division multiplexed (OFDM)symbol (or a single resource unit of an orthogonal frequency divisionmultiple access (OFDMA) symbol). For example, the single OFDM symbol mayinclude a first tone (or a first set of tones) that have a testingsequence modulated using the first MCS and a second tone (or second setof tones) that have the testing sequence modulated using the second MCS.In some implementations, each tone in the OFDM symbol may be modulatedusing a different MCS. Alternatively, or additionally, a first OFDMsymbol of the test packet may be modulated using a first MCS and asecond OFDM symbol of the test packet may be modulated using a secondMCS. This disclosure describes several formats and structures of varioustest packets that can include test portions to evaluate differenttransmission rate options. For brevity, the test portions may bedescribed in terms of a format structure of a test packet. However, thesame or similar concepts may be used in preparation of a test packetsuch that the test portions are located in various frequency domain ortime domain signals of a physical layer transmission.

In some implementations, the test packet may be a new packet formatdefined in a standard technical specification for the WLAN, such as IEEE802.11be. In some implementations, the test packet may be based on apacket format for a null data packet (NDP). In some implementations, thetest packet may be based on packet format for a data-carrying packet ora contention-based signaling packet (such as a request-to-send (RTS)packet). In some implementations, the test packet may be based on atraditional packet format that includes a padding section. The variousportions (modulated with different transmission rate options) may beincluded in a padding section at the beginning or the end of atraditional packet format. Other alternative formats for the test packetmay be possible. In some implementations, the test packet may becommunicated as an initial packet of a session so that an optimaltransmission rate may be selected for use with subsequent packets of thesession. In some implementations, a transmitting WLAN device (such as anAP) may transmit a broadcast test packet with the multiple portions(modulated with different transmission rate options) so that multipleSTAs may observe the broadcast test packet. One or more STAs may providefeedback based on the broadcast test packet. The AP may use the feedbackto determine which transmission rate option is optimal for each STA thatprovides the feedback.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. A link adaptation test packet may be used toquickly determine an optimal transmission rate option (such as an MCSoption) for subsequent transmissions without requiring a series ofpackets and repetitive transmission rate adjustments to converge on theoptimal transmission rate option between a transmitting WLAN device andthe receiving WLAN device. Throughput and resiliency may be improved byreducing error rates in transmission that would otherwise use lessoptimal transmission rate settings. In addition to saving time for linkadaptation between a pair of WLAN devices, the use of a single linkadaptation test packet to determine an optimal MCS may preserve airtimeresources that could otherwise be used for other WLAN devices.

FIG. 1 shows a pictorial diagram of an example wireless communicationnetwork 100 that supports the use of a link adaptation test packet.According to some aspects, the wireless communication network 100 can bean example of a wireless local area network (WLAN) such as a Wi-Finetwork (and will hereinafter be referred to as WLAN 100). For example,the WLAN 100 can be a network implementing at least one of the IEEE802.11 family of wireless communication protocol standards (such as thatdefined by the IEEE 802.11-2016 specification or amendments thereofincluding, but not limited to, 802.11ah, 802.11ad, 802.11ay, 802.11ax,802.11az, 802.11ba and 802.11be). The WLAN 100 may provide access toanother network 160. For example, the AP 102 may be connected to agateway device (not shown) which provides connectivity to the othernetwork 160. The WLAN 100 may include numerous wireless communicationdevices such as at least one access point (AP) 102 and multiple stations(STAs) 104 that may have a wireless association with the AP 102. Whileonly one AP 102 is shown, the WLAN network 100 also can include multipleAPs 102.

Each of the STAs 104 also may be referred to as a mobile station (MS), amobile device, a mobile handset, a wireless handset, an access terminal(AT), a user equipment (UE), a subscriber station (SS), or a subscriberunit, among other possibilities. The STAs 104 may represent variousdevices such as mobile phones, personal digital assistant (PDAs), otherhandheld devices, netbooks, notebook computers, tablet computers,laptops, display devices (for example, TVs, computer monitors,navigation systems, among others), music or other audio or stereodevices, remote control devices (“remotes”), printers, kitchen or otherhousehold appliances, key fobs (for example, for passive keyless entryand start (PKES) systems), among other possibilities.

A single AP 102 and an associated set of STAs 104 may be referred to asa basic service set (BSS), which is managed by the respective AP 102.FIG. 1 additionally shows an example coverage area 108 of the AP 102,which may represent a basic service area (BSA) of the WLAN 100. The BSSmay be identified to users by a service set identifier (SSID), as wellas to other devices by a basic service set identifier (BSSID), which maybe a medium access control (MAC) address of the AP 102. The AP 102periodically broadcasts beacon frames (“beacons”) including the BSSID toenable any STAs 104 within wireless range of the AP 102 to “associate”or re-associate with the AP 102 to establish a respective communicationlink 106 (hereinafter also referred to as a “Wi-Fi link”), or tomaintain a communication link 106, with the AP 102. For example, thebeacons can include an identification of a primary channel used by therespective AP 102 as well as a timing synchronization function forestablishing or maintaining timing synchronization with the AP 102. TheAP 102 may provide access to external networks to various STAs 104 inthe WLAN via respective communication links 106.

To establish a communication link 106 with an AP 102, each of the STAs104 is configured to perform passive or active scanning operations(“scans”) on frequency channels in one or more frequency bands (forexample, the 2.4 GHz, 5 GHz, 6 GHz or 60 GHz bands). To perform passivescanning, a STA 104 listens for beacons, which are transmitted byrespective APs 102 at a periodic time interval referred to as the targetbeacon transmission time (TBTT) (measured in time units (TUs) where oneTU may be equal to 1024 microseconds (μs)). To perform active scanning,a STA 104 generates and sequentially transmits probe requests on eachchannel to be scanned and listens for probe responses from APs 102. EachSTA 104 may be configured to identify or select an AP 102 with which toassociate based on the scanning information obtained through the passiveor active scans, and to perform authentication and associationoperations to establish a communication link 106 with the selected AP102. The AP 102 assigns an association identifier (AID) to the STA 104at the culmination of the association operations, which the AP 102 usesto track the STA 104.

As a result of the increasing ubiquity of wireless networks, a STA 104may have the opportunity to select one of many BSSs within range of theSTA or to select among multiple APs 102 that together form an extendedservice set (ESS) including multiple connected BSSs. An extended networkstation associated with the WLAN 100 may be connected to a wired orwireless distribution system that may allow multiple APs 102 to beconnected in such an ESS. As such, a STA 104 can be covered by more thanone AP 102 and can associate with different APs 102 at different timesfor different transmissions. Additionally, after association with an AP102, a STA 104 also may be configured to periodically scan itssurroundings to find a more suitable AP 102 with which to associate. Forexample, a STA 104 that is moving relative to its associated AP 102 mayperform a “roaming” scan to find another AP 102 having more desirablenetwork characteristics such as a greater received signal strengthindicator (RSSI) or a reduced traffic load.

In some cases, STAs 104 may form networks without APs 102 or otherequipment other than the STAs 104 themselves. One example of such anetwork is an ad hoc network (or wireless ad hoc network). Ad hocnetworks may alternatively be referred to as mesh networks orpeer-to-peer (P2P) networks. In some cases, ad hoc networks may beimplemented within a larger wireless network such as the WLAN 100. Insuch implementations, while the STAs 104 may be capable of communicatingwith each other through the AP 102 using communication links 106, STAs104 also can communicate directly with each other via direct wirelesslinks 111. Additionally, two STAs 104 may communicate via a directcommunication link 111 regardless of whether both STAs 104 areassociated with and served by the same AP 102. In such an ad hoc system,one or more of the STAs 104 may assume the role filled by the AP 102 ina BSS. Such a STA 104 may be referred to as a group owner (GO) and maycoordinate transmissions within the ad hoc network. Examples of directwireless links 111 include Wi-Fi Direct connections, connectionsestablished by using a Wi-Fi Tunneled Direct Link Setup (TDLS) link, andother P2P group connections.

The APs 102 and STAs 104 may function and communicate (via therespective communication links 106) according to the IEEE 802.11 familyof wireless communication protocol standards (such as that defined bythe IEEE 802.11-2016 specification or amendments thereof including, butnot limited to, 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az,802.11ba and 802.11be). These standards define the WLAN radio andbaseband protocols for the PHY and medium access control (MAC) layers.The APs 102 and STAs 104 transmit and receive wireless communications(hereinafter also referred to as “Wi-Fi communications”) to and from oneanother in the form of physical layer convergence protocol (PLCP)protocol data units (PPDUs). The APs 102 and STAs 104 in the WLAN 100may transmit PPDUs over an unlicensed spectrum, which may be a portionof spectrum that includes frequency bands traditionally used by Wi-Fitechnology, such as the 2.4 GHz band, the 5 GHz band, the 60 GHz band,the 3.6 GHz band, and the 900 MHz band. Some implementations of the APs102 and STAs 104 described herein also may communicate in otherfrequency bands, such as the 6 GHz band, which may support both licensedand unlicensed communications. The APs 102 and STAs 104 also can beconfigured to communicate over other frequency bands such as sharedlicensed frequency bands, where multiple operators may have a license tooperate in the same or overlapping frequency band or bands.

Each of the frequency bands may include multiple sub-bands or frequencychannels. For example, PPDUs conforming to the IEEE 802.11n, 802.11acand 802.11ax standard amendments may be transmitted over the 2.4 and 5GHz bands, each of which is divided into multiple 20 MHz channels. Assuch, these PPDUs are transmitted over a physical channel having aminimum bandwidth of 20 MHz, but larger channels can be formed throughchannel bonding. For example, PPDUs may be transmitted over physicalchannels having bandwidths of 40 MHz, 80 MHz, 160 or 320 MHz by bondingtogether multiple 20 MHz channels.

Each PPDU is a composite structure that includes a PHY preamble and apayload in the form of a PLCP service data unit (PSDU). The informationprovided in the preamble may be used by a receiving device to decode thesubsequent data in the PSDU. In instances in which PPDUs are transmittedover a bonded channel, the preamble fields may be duplicated andtransmitted in each of the multiple component channels. The PHY preamblemay include both a legacy portion (or “legacy preamble”) and anon-legacy portion (or “non-legacy preamble”). The legacy preamble maybe used for packet detection, automatic gain control and channelestimation, among other uses. The legacy preamble also may generally beused to maintain compatibility with legacy devices. The format of,coding of, and information provided in the non-legacy portion of thepreamble is based on the particular IEEE 802.11 protocol to be used totransmit the payload.

A STA 144 is associated with the AP 102 and can receive downstreamcommunications from, or transmit upstream communications to, the AP 102via a communication link 106. A representative downstream communicationis described in FIG. 1 . To avoid ambiguity, the AP 102 may be referredto as a first WLAN device 110. Alternatively, the first WLAN device 110may be a wireless communication device in the AP 102. Acting as thetransmitting WLAN device, the first WLAN device 110 is capable ofcommunicating the downstream data to a second WLAN device 120 (such asthe STA 144). The second WLAN device 120 may be referred to as areceiving WLAN device. Thus, in FIG. 1 , the first WLAN device 110 maybe referred to as a transmitting WLAN device and the second WLAN device120 may be referred to as a receiving WLAN device. However, thedesignations of transmitting WLAN device and receiving WLAN device maybe reversed for upstream data (from the STA 144 to the AP 102).Similarly, the techniques in this disclosure may be used withpeer-to-peer or mesh networks in which case one WLAN device may beconsidered a transmitting WLAN device and the other WLAN device may beconsidered a receiving WLAN device.

FIG. 1 also shows an example of potential interference 142 from anexternal transmitter 140 (such as a radio broadcast tower, WWAN, oranother WLAN, among other examples). The interference 142 may impactchannel conditions of the wireless channel used by the BSS managed bythe AP 102. The interference 142 may have a greater impact on a hightransmission rate (such as a first MCS) and may have a lesser impact ona low transmission rate (such as a second MCS). To provide flexibilityof transmission rates, the IEEE 802.11 family of standards specifyvarious MCS options having different modulation and coding rates. Thevarious modulation schemes may include a binary phase shift keying(BPSK) modulation scheme, a quadrature phase shift keying (QPSK)modulation scheme, and different types of a quadrature amplitudemodulation (QAM) modulation schemes, among other examples. A code ratemay refer to how much of a data stream is actually being used totransmit usable data. A higher code rate means that the datatransmission is more efficient. Meanwhile, a lower code rate may resultin a more robust transmission because the transmission may includeredundant data or error correction data. As described herein, atraditional technique for link adaptation may include an iterativeprocess to sequentially adjust the MCS selection until the WLAN devicesconverge on an optimal transmission rate that balances data throughputwith the amount of interference 142. This disclosure describes a linkadaptation technique to determine an optimal MCS between a transmittingWLAN device (such as the first WLAN device 110) and a receiving WLANdevice (such as the second WLAN device 120).

The first WLAN device 110 may include a link adaptation test packettransmission unit 152. The link adaptation test packet transmission unit152 may be configured to transmit a first packet (which may be referredto as a link adaptation test packet 172) to the second WLAN device 120.In some implementations, the link adaptation test packet 172 may beformatted as a single user (SU) basic open loop transmission.Alternatively, the link adaptation test packet 172 may be formatted asmulti-user (MU) transmission such as an OFDMA or MU-MIMO transmission.For brevity, the link adaptation test packet 172 described withreference to FIG. 1 is formatted as an SU transmission from the firstWLAN device 110 to the second WLAN device 120. The link adaptation testpacket 172 may include a plurality of test portions that are modulatedusing a corresponding plurality of MCS options. For example, a firstportion may be modulated using a first MCS and a second portion may bemodulated using a second MCS. Thus, a single link adaptation test packet172 may support testing of a several MCS options based on currentchannel conditions. Example MCS options are described with reference toFIG. 4 . The portions may be based on a time division, frequencydivision, spatial stream division, or other basis that can be delineatedin the first packet. A predetermined testing sequence (such as a bitsequence or pattern) may be used as a consistent source signal for allof the test portions. Thus, the testing signal may be common to all thetest portions, such that the MCS option may be the only variabledifference between the test portions. In some implementations, the linkadaptation test packet 172 also may carry data other than the testportions.

The first WLAN device 110 may include a link adaptation unit 154 that isconfigured to determine a transmission rate or other link configurationfor a subsequent packet 176 for transmission to the second WLAN device120. For example, the link adaptation unit 154 may receive feedbackinformation 174 from the second WLAN device 120 in response to the linkadaptation test packet 172. The link adaptation unit 154 may determine aselected MCS to use for the subsequent packet 176 based on the feedbackinformation 174. In some implementations, the feedback information 174may include link quality metrics regarding each MCS option in the linkadaptation test packet 172. Alternatively, or additionally, the feedbackinformation 174 may include an MCS indicator that indicates the MCSoption selected by the second WLAN device 120 based on the linkadaptation test packet 172. After the selected MCS option is determinedby the link adaptation unit 154, the first WLAN device 110 may transmitsubsequent packets 176 using the selected MCS option. Although describedin terms of an MCS option, the transmission rate option selected by thelink adaptation unit 154 may be any parameter that adapts thetransmission rate based on current channel conditions. A datatransmission unit 156 in the first WLAN device 110 may modulate thesubsequent packet 176 using the transmission rate option selected by thelink adaptation unit 154 based on the feedback information 174 regardingthe link adaptation test packet 172.

The second WLAN device 120 may include a link adaptation test packetprocessing unit 162. The link adaptation test packet processing unit 162may receive the link adaptation test packet 172 and determine linkquality metrics for the various test portions in the link adaptationtest packet 172. For example, the link adaptation test packet processingunit 162 may process each portion separately to determine a receivedtesting signal for each test portion. The link adaptation test packetprocessing unit 162 may determine the link quality metrics based oncomparisons of the received testing signal with the predeterminedtesting signal that was used by the first WLAN device 110 for each testportion. Thus, the predetermined testing signal may be a known sequenceor pattern that the link adaptation test packet processing unit 162 thatcan be compared with the received testing signal to determine a BER,BLER, SNR, SINR, or EVM, among other examples.

The second WLAN device 120 may include a feedback unit 164 configured toprepare the feedback information 174. The feedback unit 164 may selectan MCS option based on the quality metrics determined by the linkadaptation test packet processing unit 162. Alternatively, the feedbackunit 164 may prepare a feedback message that includes the qualitymetrics. A data reception unit 166 in the second WLAN device 120 mayreceive and process the subsequent packet 176 based on a selectedtransmission rate option (such as a selected MCS option).

FIG. 2 depicts an example link adaptation protocol that uses a linkadaptation test packet. The example link adaptation protocol 200 maybegin with a first packet 210 from the first WLAN device 110 to thesecond WLAN device 120. The first packet 210 may include an indicator toindicate that the first packet includes multiple test portions 201. Forexample, in some implementations, the first packet 210 may include alink adaptation testing capability or enablement indicator to indicatethat the first packet 210 is formatted for use in the link adaptationprotocol 200. In some implementations, a testing header in the firstpacket 210 may indicate which transmission rate options are used for thetest portions 201. The transmission rate options may be various MCSoptions. In the example of FIG. 2 , the first packet 210 includes afirst portion 270 modulated using a first MCS option, a second portion280 modulated using a second MCS option, and a third portion 290modulated using a third MCS option.

Upon receiving the first packet 210, the second WLAN device 120 maydetermine a success or error rate for each of the test portions 201 todetermine which MCS option had a highest throughput and quality above athreshold value. For example, if the first portion 270 and the secondportion 280 were both received with a quality above the threshold value,the second WLAN device 120 may determine which MCS option (for the firstportion 270 and the 280) would result in a highest data throughput.Meanwhile, if the third portion 290 was received with a quality belowthe threshold value (such as a high bit error rate indicating lowerquality), the second WLAN device 120 may determine that the third MCSoption should not be used for a subsequent packet. A low quality MCS mayresult in retransmissions which consume airtime and result in additionalprocessing overhead. Meanwhile, if multiple MCS options result in aquality metric above the quality threshold, the optimal MCS option isthe one that would result in the highest throughput while havingacceptable quality above the threshold value.

In response to the first packet 210, the second WLAN device 120 may senda feedback message 230 back to the first WLAN device 110. The feedbackmessage 230 may begin after a short interframe space (SIFS) 220, whichrepresents a determinable time period to maintain synchronization in theWLAN. The feedback message 230 may indicate the quality metricsregarding the test portions 201 or may indicate the optimal transmissionrate option selected by the second WLAN device 120 based on the qualityand throughput. Based on the feedback information in the feedbackmessage 230, the first WLAN device 110 may determine a selectedtransmission rate option to use for all or part of a second packet 240transmitted from the first WLAN device 110 to the second WLAN device120.

FIG. 3 depicts an example message flow diagram of a link adaptationprotocol using a link adaptation test packet. The example message flow300 shows the first WLAN device 110 (as the transmitting WLAN device)and the second WLAN device 120 (as the receiving WLAN device). The firstWLAN device 110 and the second WLAN device 120 may exchangeconfiguration messages 312 to establish a wireless association over awireless communication medium.

The first WLAN device 110 may transmit a first packet 322 to the secondWLAN device 120. The first packet 322 may include multiple test portionsthat include the same predetermined testing signal modulated usingdifferent transmission rate options. The second WLAN device 120 mayprocess (shown at block 324) the first packet 322 to determine qualitymetrics regarding the test portions as described above. The second WLANdevice 120 may transmit feedback information 326 to the first WLANdevice 110 based on the first packet 322. Based on the feedbackinformation 326, the first WLAN device 110 may determine a selectedtransmission rate option (such as an MCS) to use for transmission ofsubsequent packets 328 to the second WLAN device 120.

FIG. 4 shows an example link adaptation test packet and examplecorresponding MCS options. The link adaptation test packet 400 mayinclude a testing header 405 and multiple test portions 410, 420, 430,and 440. Although only four test portions are depicted in FIG. 4 , thequantity of test portions may be different. For example, in someimplementations, the link adaptation test packet 400 may include a testportion for each MCS option defined by a standard technicalspecification for the WLAN.

The chart 401 in FIG. 4 shows example MCS options. The chart 401 showsfourteen MCS options (numbered MCS 0 to MCS 13), each having a differentcombination of modulation scheme and forward error correction (FEC) coderate (sometimes referred to as code rate). The various modulationschemes may include a binary phase shift keying (BPSK) modulationscheme, a quadrature phase shift keying (QPSK) modulation scheme, anddifferent types of a quadrature amplitude modulation (QAM) modulationschemes, among other examples. The forward error correction code ratemay impact how much of a data stream is actually being used to transmitusable data. For example, a code rate of 5/6 means that 83.3% of atransmitted data stream includes actual data (or every five out of sixbits are information bits with the remaining bits are parity bits). Ahigher code rate means that the data transmission is more efficient.Meanwhile, a lower code rate may result in a more robust transmissionbecause the transmission may include redundant data or error correctiondata, among other examples. Based on the chart 401, the data throughputmay increase as a number for the MCS option increases. For example, MCS13 has a higher data throughput than MCS 0. However, the higher numberedMCS options are more susceptible to errors caused by interference orpoor radio conditions.

In some implementations, the testing header 405 may signal to thereceiving WLAN device that the link adaptation test packet 400 includesthe test portions 410, 420, 430, and 440. Additionally, oralternatively, the testing header 405 may indicate which MCS options areused to modulate the different test portions 410, 420, 430, and 440. Inthe example of FIG. 4 , a first portion 410 includes a known testingsignal that is modulated using MCS 5 (which refers to a combination of a64QAM modulation scheme and a 2/3 code rate). A second portion 420includes the same known testing signal that is modulated using MCS 8(which refers to a combination of a 256QAM modulation scheme and a 3/4code rate). A third portion 430 includes the same known testing signalthat is modulated using MCS 10 (which refers to a combination of a1024QAM modulation scheme and a 3/4 code rate). A fourth portion 440includes the same known testing signal that is modulated using MCS 13(which refers to a combination of a 4096QAM modulation scheme and a 5/6code rate). Thus, a single link adaptation test packet 400 may be usedto determine which MCS option results in an optimal data throughputbased on current wireless channel conditions.

FIG. 5A depicts a first example feedback message format. The firstexample feedback message format 500 may be based on a legacy preambleassociated with legacy WLAN frame format 502. The feedback messageformat 500 may include a legacy short training field 504 (L-STF), alegacy long training field 506 (L-LTF), and a legacy signal field 508(L-SIG). The L-STF and the L-LTF are used for detection andsynchronization using predetermined training signals. Thus, the L-SIGfield is the only portion of the legacy preamble which carries data. TheL-SIG field includes a set of bits for indicating a rate setting 512 anda set of bits for indicating a length 514 of the legacy WLAN packet thatwould normally follow the legacy preamble. In the example, of FIG. 5A,the feedback message may end with the L-SIG. Therefore, the length 514may indicate a value of “0.” The rate setting 512 may indicate aselected MCS option determined by the receiving WLAN device based onquality metrics for the test portions of a link adaptation test packet.

FIG. 5B depicts a second example feedback message format. The secondexample feedback message format 501 may be based on a legacy preamble(L-STF 504, L-LTF 506, and L-SIG 508) followed by feedback information538. There may be different subfields in the feedback information 538.FIG. 5B shows several example feedback subfields 560, including a testportions quality metrics 562, a selected transmission rate optionindicator 564, and test results bitmap 566. The test portions qualitymetrics 562 may indicate quality metrics for each test portion. Forexample, the test portions quality metrics 562 may include a BER, BLER,SINR, SNR, EVM, or other quality metric which indicates how well thereceived test signal for each test portion compares with the known testsignal. The selected transmission rate option indicator 564 may indicatea selected MCS or other transmission rate parameter chosen by thereceiving WLAN device based on analyzing the test portions of a linkadaptation test packet. The test results bitmap 566 may indicate whichtest portions were successfully decoded. For example, each bit in thebitmap may provide a success or failure indication for each testportion. A first value (zero) may indicate that the test portion was notsuccessfully decoded (or was received with a low quality). A secondvalue (one) may indicate that the test portion was successfully decoded(and was received with a high quality). The examples in FIGS. 5A and 5Bare intended as illustrative examples, and other variations may bepossible.

FIG. 6A depicts a block diagram of an example transmitting WLAN devicethat supports link adaptation. The example transmitting WLAN device 600is one of many designs for a first WLAN device. The example transmittingWLAN device 600 is based on a transmitter that supports transmission ofuser data as well as a link adaptation testing signal. The transmittingWLAN device 600 is designed for binary convolutional coding (BCC)encoding. Another design (not shown) may support low data parity check(LDPC) encoding. The transmitting WLAN device 600 in FIG. 6A supportsthe transmission of data 602. The data 602 may be processed by ascrambler 610 and an encoding module 615. The scrambler 610 may scramblethe data 602 to reduce the probability of long sequences of zeros orones. The scrambler 610 may use a seed to determine the scrambled bits.The seed may be known or shared with the receiving WLAN device so thatthe receiving WLAN device can reverse the scrambling process performedby the scrambler 610. After scrambling, the data may be processed by theencoding module 615.

In the design described in FIG. 6A, a testing signal generator 605 maysend one or more copies of a predetermined testing signal for processingby the transmitter apparatus. The testing signal may be sent in lieu ofthe data 602, or may be sent for encoding in part of a same packet thatincludes the data 602. The predetermined testing signal may be processedby the encoding module 615. In some implementations, the testing signalmay be a known sequence that can be designed to avoid the need toscramble the bits. Therefore, in some implementations, the testingsignal may not be processed by the scrambler 610.

The encoding module 615 may perform encoding for error correction anderror detection. For example, the encoding module 615 may perform FECand add redundancy or CRC bits to the source data. The encoder may useBCC to encode the data. The encoded data may be sent to a stream parser620 that divides the encoded data into N_(SS) spatial streams. In someimplementations, there may only be one spatial stream and the streamparser 620 may be unused. An example of spatial stream processing 640may include an interleaver 630, and a constellation mapper 635. Theinterleaver 630 interleaves the bits of each spatial stream (changesorder of bits) to prevent long sequences of adjacent noisy bits fromentering the BCC decoder. The interleaver 630 may be present intransmitter designs that use BCC encoding. When LDPC encoding is used(rather than BCC), the interleaver 630 may be omitted. Interleaving isapplied only when BCC encoding is used. The constellation mapper 635maps the sequence of bits in each spatial stream to constellation points(complex numbers). The constellation mapper 635 may perform themodulation of the bits based on the selected MCS option. For example,the constellation mapper 635 may determine the constellation points formodulation based on a modulation scheme for the MCS option. For eachportion of the link adaptation test packet, the constellation mapper 635may use a different MCS option.

After the spatial streams are processed, a spatial mapping 645 may mapspace-time streams to N_(TX) transmit chains (including TX chain 650).There may be different ways of mapping the streams to transmit chains.For example, in a direct mapping the constellation points from eachspace-time stream may be mapped directly onto the transmit chains(one-to-one mapping). Another example may use spatial expansion, inwhich vectors of constellation points from all the space-time streamsare expanded via matrix multiplication to produce the input to all ofthe transmit chains. The spatial mapping 645 may support beamforming(like spatial expansion), in which each vector of constellation pointsfrom all of the space-time streams is multiplied by a matrix of steeringvectors to produce the input to the transmit chains.

Each TX chain 650 may prepare a plurality of OFDM symbols based on theconstellation points. For example, the TX chain 650 may include aninverse discrete Fourier transform (IDFT) that converts a block ofconstellation points to a time domain block. The TX chain 650 mayinclude a cyclic shift (CSD), guard interval inserter, and an analogfront end to transmit OFDM symbols as radio frequency (RF) energy.

The transmitting WLAN device 600 described in FIG. 6A is only oneexample of a transmitter apparatus. Other block diagrams may add orremove functional blocks.

FIG. 6B depicts a block diagram of an example receiving WLAN device thatsupports a link adaptation. The example receiving WLAN device 601 is oneof many possible designs for second WLAN device. In the example of FIG.6B, RF energy may be received by an analog front end of a receive (RX)chain 655. For example, the RX chain 655 may include an antenna andautomatic gain control (AGC) components (not shown). Furthermore, the RXchain 655 may include a fast Fourier transform (FFT) function to converttime domain symbols to a frequency domain representation of receiveddata. N_(RX) receive chains may prepare frequency domain representationsof received data associated with each RX chain. Each spatial stream maybe processed by a demodulation module 660. In accordance with thisdisclosure, the demodulation module 660 may use different MCS options todemodulate different portions of the link adaptation test packet. Thedemodulation module 660 may convert the frequency domain representationsinto a plurality of spatial streams. As a result, the demodulationmodule 660 may provide N_(SS) spatial streams. An example of spatialstream processing 672 may include a deinterleaver 665 and a demodulator672. If BCC interleaver was used in the transmitting WLAN device 600,the deinterleaver 665 may perform a de-interleaving of the bitstream torecover an original ordering of the bitstream. The demodulator 670 mayuse LLR calculations to recover a bit stream. A stream combiner 675 mayreverse the process of the stream parser 620 of the transmitter. Forexample, the stream combiner 675 may combine bitstreams from multiplespatial streams to prepare encoded data bits for a decoding module 680.The decoding module 680 may decode the encoded bits. In someimplementations, the decoding module 680 may implement error correctionusing redundancy bits in the encoded bits. The decoding module 680 maysend a received testing signal to a testing signal comparator 695. Thetesting signal comparator 695 may compare the received testing signalfor each test portion with the known testing signal to determine afidelity or quality metric associated with the test portion.

In some implementations, the example receiving WLAN device 601 may beconfigured to receive data 698 in addition to the testing signal. Thedecoding module 680 may send received data to a descrambler 690. Thedescrambler 690 may reverse the scrambling performed by the scrambler inthe transmitting WLAN device. The descrambler 690 may provide thereceived data 698 to an upper layer (not shown) of the example receivingWLAN device 601.

FIG. 7 depicts an example link adaptation test packet 700 using timedivision for test portions. For example, the link adaptation test packet700 can be formatted as a PPDU. As shown, the link adaptation testpacket 700 includes a preamble and the test collection 712. For example,the preamble may be a PHY preamble and may include a legacy portion thatitself includes a legacy short training field (L-STF) 704, a legacy longtraining field (L-LTF) 706, and a legacy signaling field (L-SIG) 708.The preamble also may include a non-legacy portion (not shown). TheL-STF 704 generally enables a receiving device to perform automatic gaincontrol (AGC) and coarse timing and frequency estimation. The L-LTF 706generally enables a receiving device to perform fine timing andfrequency estimation and also to estimate the wireless channel. TheL-SIG 708 generally enables a receiving device to determine a durationof the PPDU and use the determined duration to avoid transmitting on topof the PPDU. For example, the L-STF 704, the L-LTF 706 and the L-SIG 708may be modulated using a robust MCS option, such as one that uses a BPSKmodulation scheme. Following the preamble, the link adaptation testpacket 700 may include one or more other headers (not shown) and testcollection 712. The test collection 712 may include a testing header 720to indicate which MCS options are used to modulate the test portions721, 722, and 723. The test portions 721, 722, and 723 may be based onthe same testing sequence 740 but modulated using different MCS options.As shown in FIG. 7 , the test portions may be ordered in time divisionin the test collection 712 section of the link adaptation test packet700. In some implementations, each test portion may be one or more OFDMsymbols in a series of OFDM symbols that make up the link adaptationtest packet 700.

FIG. 8 depicts an example link adaptation test packet 800 in which thetesting portions are included in a padding section of a data carryingpacket. Similar to the link adaptation test packet 700, the linkadaptation test packet 800 may include a preamble (such as the L-STF704, the L-LTF 706, and the L-SIG 708). However, different from the linkadaptation test packet 700, the link adaptation test packet 800 may be adata carrying packet that includes a data payload 810. For example, thedata payload 810 may include data for the second WLAN device. The datapayload 810 may be modulated by a less optimal MCS option or may bemodulated based on a previously selected MCS option. Following the datapayload 810, typically the PPDU would include a padding section 812.However, in some implementations, the padding section 812 maybepopulated with the test portions (such as the test collection 712 asdescribed with reference to FIG. 7 ). Although illustrated as followingthe data payload 810 in FIG. 8 , in some implementations the testcollection 712 may be included before data payload 810. The data payload810 may be a separate portion that is different from the test portionsin the test packet.

FIG. 9A shows an example conceptual diagram in which an OFDM symbolincludes multiple link adaptation test portions. The OFDM channel widthmay include multiple subcarriers. The subcarriers also may be referredto as tones. A WLAN packet (also referred to as a PPDU) includes datathat is encoded using the subcarriers of the channel width. A PPDU maybe different lengths of time and include multiple OFDM symbols. In someimplementations, a transmitting WLAN device may include one OFDM symbol(such as OFDM symbol 950) that has different test portions modulatedusing a different MCS. For example, the OFDM symbol 950 in FIG. 9Aincludes four test portions 912, 922, 932, and 942 which may be referredto as test portion 1 (TP1), TP2, TP3, and TP4, respectively. Each testportion may be modulated using a different MCS so that a variety of MCSoptions can be included in the OFDM symbol 950. Each test portions maybe a set of contiguous subcarriers (as shown in FIG. 9A) or may be a setof non-contiguous subcarriers (so that the full channel width may havedifferent subcarriers modulated with the MCS option for each testportion). In some implementations, the test portions may be made up ofonly one subcarrier each. For example, the test portions TP1, TP2, TP3,and TP4 may be one subcarrier each. The remaining subcarriers may beused for data or other signaling.

FIG. 9B shows an example conceptual diagram in which multiple OFDMsymbols may be used for a link adaptation test packet. For example, afirst OFDM symbol 910 may include a first test portion (TP1) 912. Asecond OFDM symbol 920 may include a second test portion (TP2) 922. Athird OFDM symbol 930 may include a third test portion (TP3) 932. Afourth OFDM symbol 940 may include a fourth test portion (TP4) 942. Eachof the test portions 912, 922, 932, and 942 may be modulated with adifferent MCS.

FIG. 9C shows an example conceptual diagram in which the test portionsare included in a resource unit of an OFDMA transmission. IEEE 802.11axintroduced the use of OFDMA in a WLAN. OFDMA breaks down the channelwidth into a plurality of resource units (RUs). Each RU may include adifferent quantity of subcarriers. Using OFDMA, an AP may allocatedifferent RUs for different WLAN devices. For example, a PPDU 960 mayinclude different RUs allocated for a first WLAN device, a second WLANdevice, a third WLAN device, and a fourth WLAN device. One RU 970 may beallocated for a first WLAN device in the PPDU 960, while other RUs 972and 974 are allocated for different WLAN devices. The allocation of RUsalso may be used to schedule channel access. For example, a triggermessage from an AP may indicate which RUs are allocated to particularSTAs to use for uplink traffic in the PPDU that follows the triggermessage.

In the example shown in FIG. 9C, a first RU 970 may include linkadaptation test portions from a first WLAN device (such as an AP) to asecond WLAN device (such as a STA). Thus, the RU 970 may be divided byfrequency division to support different test portions 912, 922, 932, and942. The test portions 912, 922, 932, and 943 may occupy different tones(or sets of tones) within the RU 970. Each test portion may be modulatedusing a different MCS option.

The concepts described in FIGS. 9A, 9B, and 9C are illustrative examplesand are not mutually exclusive. For example, when a PPDU includesmultiple OFDM symbols, each OFDM symbol may carry user data or othersignaling in some subcarriers and a test portion in other subcarriers.Furthermore, a series of OFDM symbols may be used to communicate testportions which occupy subsets of the subcarriers in each OFDM symbol.The quantity and size of the test portions in FIGS. 9A-9C may vary andmay depend on the quantity of MCS options being evaluated in the linkadaptation test packet.

FIG. 10 shows a flowchart illustrating an example process 1000 bytransmitting WLAN device to support link adaptation. In someimplementations, the process 1000 may be performed by a first WLANdevice such as the AP 102 described above. In some implementations, theprocess 1000 begins in block 1010.

In block 1010, a first WLAN device may transmit a first packet from afirst WLAN device to a second WLAN device via a wireless channel. Thefirst packet may include a plurality of link adaptation test portionsgenerated using a corresponding plurality of transmission rate options.For example, a first portion may be modulated using a first MCS and asecond portion may be modulated using a second MCS.

In block 1020, the first WLAN device may receive, from the second WLANdevice, feedback information based on the plurality of link adaptationtest portions in the first packet.

In block 1030, the first WLAN device may determine a selectedtransmission rate option for transmission of a subsequent packet to thesecond WLAN device via the wireless channel based, at least in part, onthe feedback information.

In some implementations, each of the plurality of link adaptation testportions is modulated using a different MCS option. The feedbackinformation may include an LLR metric indicative of a decoding successrate for each of the plurality of link adaptation test portions.Alternatively, or additionally, the feedback information may include alink quality metric (such as SINR or EVM) that is indicative of a linkquality associated with each of the plurality of link adaptation testportions. In some implementations, the first WLAN device may select anMCS option associated with a link adaptation test portion having ahighest throughput and for which the corresponding LLR metric is above athreshold.

FIG. 11 shows a flowchart illustrating an example process 1100 by areceiving WLAN device to support link adaptation. In someimplementations, the process 1100 may be performed by a second WLANdevice such as second WLAN device 120 described above. In someimplementations, the process 1100 begins in block 1110. In block 1110,the second WLAN device may receive, from a first WLAN device via awireless channel, a first packet that includes a plurality of linkadaptation test portions generated using a corresponding plurality oftransmission rate options. For example, a first portion may be modulatedusing a first MCS and a second portion may be modulated using a secondMCS.

In block 1120, the second WLAN device may transmit feedback informationto the first WLAN device based on the plurality of link adaptation testportions in the first packet. The feedback information may be usable bythe first WLAN device to determine a selected transmission rate optionfor transmission of a subsequent packet from the first WLAN device viathe wireless channel.

FIG. 12 shows a block diagram of an example wireless communicationdevice 1200. In some implementations, the wireless communication device1200 can be an example of a device for use in a STA such as one of theSTAs 104 or 144 described above with reference to FIG. 1 . In someimplementations, the wireless communication device 1200 can be anexample of a device for use in an AP such as the AP 102 described abovewith reference to FIG. 1 . The wireless communication device 1200 may beused as a transmitting WLAN device or receiving WLAN device (such as thefirst WLAN device 110 and the second WLAN device 120, respectively). Thewireless communication device 1200 is capable of transmitting (oroutputting for transmission) and receiving wireless communications (forexample, in the form of wireless packets). For example, the wirelesscommunication device can be configured to transmit and receive packetsin the form of physical layer convergence protocol (PLCP) protocol dataunits (PPDUs) and medium access control (MAC) protocol data units(MPDUs) conforming to an IEEE 802.11 wireless communication protocolstandard, such as that defined by the IEEE 802.11-2016 specification oramendments thereof including, but not limited to, 802.11ah, 802.11ad,802.11ay, 802.11ax, 802.11az, 802.11ba and 802.11be.

The wireless communication device 1200 can be, or can include, a chip,system on chip (SoC), chipset, package or device that includes one ormore modems 1202, for example, a Wi-Fi (IEEE 802.11 compliant) modem. Insome implementations, the one or more modems 1202 (collectively “themodem 1202”) additionally include a WWAN modem (for example, a 3GPP 4GLTE or 5G compliant modem). In some implementations, the wirelesscommunication device 1200 also includes one or more radios 1204(collectively “the radio 1204”). In some implementations, the wirelesscommunication device 1200 further includes one or more processors,processing blocks or processing elements 1206 (collectively “theprocessor 1206”) and one or more memory blocks or elements 1208(collectively “the memory 1208”).

The modem 1202 can include an intelligent hardware block or device suchas, for example, an application-specific integrated circuit (ASIC) amongother possibilities. The modem 1202 is generally configured to implementa PHY layer. For example, the modem 1202 is configured to modulatepackets and to output the modulated packets to the radio 1204 fortransmission over the wireless medium. The modem 1202 is similarlyconfigured to obtain modulated packets received by the radio 1204 and todemodulate the packets to provide demodulated packets. In addition to amodulator and a demodulator, the modem 1202 may further include digitalsignal processing (DSP) circuitry, automatic gain control (AGC), acoder, a decoder, a multiplexer and a demultiplexer. For example, whilein a transmission mode, data obtained from the processor 1206 isprovided to a coder, which encodes the data to provide encoded bits. Theencoded bits are then mapped to points in a modulation constellation(using a selected MCS) to provide modulated symbols. The modulatedsymbols may then be mapped to a number NSS of spatial streams or anumber NSTS of space-time streams. The modulated symbols in therespective spatial or space-time streams may then be multiplexed,transformed via an inverse fast Fourier transform (IFFT) block, andsubsequently provided to the DSP circuitry for Tx windowing andfiltering. The digital signals may then be provided to adigital-to-analog converter (DAC). The resultant analog signals may thenbe provided to a frequency upconverter, and ultimately, the radio 1204.In implementations involving beamforming, the modulated symbols in therespective spatial streams are precoded via a steering matrix prior totheir provision to the IFFT block.

While in a reception mode, digital signals received from the radio 1204are provided to the DSP circuitry, which is configured to acquire areceived signal, for example, by detecting the presence of the signaland estimating the initial timing and frequency offsets. The DSPcircuitry is further configured to digitally condition the digitalsignals, for example, using channel (narrowband) filtering, analogimpairment conditioning (such as correcting for I/Q imbalance), andapplying digital gain to ultimately obtain a narrowband signal. Theoutput of the DSP circuitry may then be fed to the AGC, which isconfigured to use information extracted from the digital signals, forexample, in one or more received training fields, to determine anappropriate gain. The output of the DSP circuitry also is coupled withthe demodulator, which is configured to extract modulated symbols fromthe signal and, for example, compute the logarithm likelihood ratios(LLRs) for each bit position of each subcarrier in each spatial stream.The demodulator is coupled with the decoder, which may be configured toprocess the LLRs to provide decoded bits. The decoded bits from all ofthe spatial streams are then fed to the demultiplexer fordemultiplexing. The demultiplexed bits may then be descrambled andprovided to the MAC layer (the processor 1206) for processing,evaluation, or interpretation.

The radio 1204 generally includes at least one radio frequency (RF)transmitter (or “transmitter chain”) and at least one RF receiver (or“receiver chain”), which may be combined into one or more transceivers.For example, the RF transmitters and receivers may include various DSPcircuitry including at least one power amplifier (PA) and at least onelow-noise amplifier (LNA), respectively. The RF transmitters andreceivers may, in turn, be coupled to one or more antennas. For example,in some implementations, the wireless communication device 1200 caninclude, or be coupled with, multiple transmit antennas (each with acorresponding transmit chain) and multiple receive antennas (each with acorresponding receive chain). The symbols output from the modem 1202 areprovided to the radio 1204, which then transmits the symbols via thecoupled antennas. Similarly, symbols received via the antennas areobtained by the radio 1204, which then provides the symbols to the modem1202.

The processor 1206 can include an intelligent hardware block or devicesuch as, for example, a processing core, a processing block, a centralprocessing unit (CPU), a microprocessor, a microcontroller, a digitalsignal processor (DSP), an application-specific integrated circuit(ASIC), a programmable logic device (PLD) such as a field programmablegate array (FPGA), discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. The processor 1206 processes information receivedthrough the radio 1204 and the modem 1202, and processes information tobe output through the modem 1202 and the radio 1204 for transmissionthrough the wireless medium. For example, the processor 1206 mayimplement a control plane and MAC layer configured to perform variousoperations related to the generation and transmission of MPDUs, framesor packets. The MAC layer is configured to perform or facilitate thecoding and decoding of frames, spatial multiplexing, space-time blockcoding (STBC), beamforming, and OFDMA resource allocation, among otheroperations or techniques. In some implementations, the processor 1206may generally control the modem 1202 to cause the modem to performvarious operations described above.

The memory 1208 can include tangible storage media such as random-accessmemory (RAM) or read-only memory (ROM), or combinations thereof. Thememory 1208 also can store non-transitory processor- orcomputer-executable software (SW) code containing instructions that,when executed by the processor 1206, cause the processor to performvarious operations described herein for wireless communication,including the generation, transmission, reception and interpretation ofMPDUs, frames or packets. For example, various functions of componentsdisclosed herein, or various blocks or steps of a method, operation,process or algorithm disclosed herein, can be implemented as one or moremodules of one or more computer programs.

FIG. 13A shows a block diagram of an example AP 1302. For example, theAP 1302 can be an example implementation of the AP 102 described withreference to FIG. 1 . The AP 1302 includes a wireless communicationdevice (WCD) 1310 (although the AP 1302 may itself also be referred togenerally as a wireless communication device as used herein). Forexample, the wireless communication device 1310 may be an exampleimplementation of the wireless communication device 1200 described withreference to FIG. 12 . The AP 1302 also includes multiple antennas 1320coupled with the wireless communication device 1310 to transmit andreceive wireless communications. In some implementations, the AP 1302additionally includes an application processor 1330 coupled with thewireless communication device 1310, and a memory 1340 coupled with theapplication processor 1330. The AP 1302 further includes at least oneexternal network interface 1350 that enables the AP 1302 to communicatewith a core network or backhaul network to gain access to externalnetworks including the Internet. For example, the external networkinterface 1350 may include one or both of a wired (for example,Ethernet) network interface and a wireless network interface (such as aWWAN interface). Ones of the aforementioned components can communicatewith other ones of the components directly or indirectly, over at leastone bus. The AP 1302 further includes a housing that encompasses thewireless communication device 1310, the application processor 1330, thememory 1340, and at least portions of the antennas 1320 and externalnetwork interface 1350.

FIG. 13B shows a block diagram of an example STA 1304. For example, theSTA 1304 can be an example implementation of the STA 104 described withreference to FIG. 1 . The STA 1304 includes a wireless communicationdevice 1315 (although the STA 1304 may itself also be referred togenerally as a wireless communication device as used herein). Forexample, the wireless communication device 1315 may be an exampleimplementation of the wireless communication device 1200 described withreference to FIG. 12 . The STA 1304 also includes one or more antennas1325 coupled with the wireless communication device 1315 to transmit andreceive wireless communications. The STA 1304 additionally includes anapplication processor 1335 coupled with the wireless communicationdevice 1315, and a memory 1345 coupled with the application processor1335. In some implementations, the STA 1304 further includes a userinterface (UI) 1355 (such as a touchscreen or keypad) and a display1365, which may be integrated with the UI 1355 to form a touchscreendisplay. In some implementations, the STA 1304 may further include oneor more sensors 1375 such as, for example, one or more inertial sensors,accelerometers, temperature sensors, pressure sensors, or altitudesensors. Ones of the aforementioned components can communicate withother ones of the components directly or indirectly, over at least onebus. The STA 1304 further includes a housing that encompasses thewireless communication device 1315, the application processor 1335, thememory 1345, and at least portions of the antennas 1325, UI 1355, anddisplay 1365.

FIGS. 1-13B and the operations described herein are examples meant toaid in understanding example implementations and should not be used tolimit the potential implementations or limit the scope of the claims.Some implementations may perform additional operations, feweroperations, operations in parallel or in a different order, and someoperations differently.

While the aspects of the disclosure have been described in terms ofnumerous examples, any combination of aspects from any of the examplesis also within the scope of the disclosure. The examples in thisdisclosure are provided for pedagogical purposes. Alternatively, or inaddition to the other examples described herein, examples include anycombination of the following implementation options.

An innovative aspect of the subject matter described in this disclosurecan be implemented as a method performed by a first WLAN device. Themethod may include outputting, for transmission from a first WLAN deviceto a second WLAN device via a wireless channel, a first packet thatincludes a plurality of portions modulated using a correspondingplurality of modulation and coding scheme MCS options. A first portionmay be modulated using a first MCS and a second portion may be modulatedusing a second MCS. The method may include receiving, from the secondWLAN device, feedback information in response to the first packet. Thefeedback information may be usable by the first WLAN device to determinea selected MCS to modulate a subsequent packet for transmission to thesecond WLAN device via the wireless channel.

In some implementations, the first packet is an MCS testing packet.

In some implementations, the first packet has a format based on an NDPdefined for the WLAN.

In some implementations, the first packet includes at least oneindicator requesting the feedback information.

In some implementations, the first packet includes upper layer data forthe second WLAN.

In some implementations, the first portion and the second portion areappended as a padding section before or after the upper layer data inthe first packet.

In some implementations, the first packet includes an indictor to causethe second WLAN device to receive the first portion of the first packetusing the first MCS and the second portion of the first packet using thesecond MCS.

In some implementations, the first portion is modulated in a first setof tones of an OFDM symbol and the second portion is modulated in secondset of tones of the same OFDM symbol.

In some implementations, the plurality of portions is modulated usingthe corresponding plurality of MCS options in the same OFDM symbol.

In some implementations, the first portion and the second portion of thefirst packet are modulated in different orthogonal frequency divisionmultiplexed OFDM symbols.

In some implementations, the first packet includes a series of OFDMsymbols, each OFDM symbol being modulated using a different MCS.

In some implementations, the feedback information includes a field thatindicates the selected MCS that was selected by the second WLAN device.

In some implementations, the feedback information includes one or morequality metrics related to the first and second portions. The method mayinclude determining, by the first WLAN device, the selected MCS based onthe one or more quality metrics.

In some implementations, the one or more quality metrics may include alog-likelihood ratio (LLR), a signal to noise ratio (SNR), a signal tointerference plus noise ratio (SINR), an error vector magnitude (EVM),or any combination thereof.

In some implementations, receiving the feedback information includesreceiving an acknowledgement (ACK) message in response to the firstpacket. The ACK message may include a field populated with the feedbackinformation.

In some implementations, receiving the feedback information includesreceiving a clear to send (CTS) message in response to the first packet.The CTS message may include a field populated with the feedbackinformation.

In some implementations, the first packet is a request to send (RTS)packet.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as a method performed by a second WLANdevice. The method may include receiving, from a first WLAN device via awireless channel, a first packet that includes a plurality of portionsmodulated using a corresponding plurality of MCS options. A firstportion may be modulated using a first MCS and a second portion may bemodulated using a second MCS. The method may include outputting, fortransmission to the first WLAN device, feedback information in responseto the first packet. The feedback information may be usable by the firstWLAN device to determine a selected MCS to modulate a subsequent packetfor transmission from the first WLAN device via the wireless channel.

In some implementations, the method may include determining one or morefirst quality metrics based on the first portion of the first packet.The method may include determining one or more second quality metricsbased on the second portion of the first packet.

In some implementations, the method may include determining the feedbackinformation based on the one or more first quality metrics and the oneor more second quality metrics. The feedback information may include aplurality of quality metrics that correspond to the plurality ofportions of the first packet.

In some implementations, the method may include determining the selectedMCS based on the one or more first quality metrics and the one or moresecond quality metrics. The feedback information may include a fieldthat indicates the selected MCS.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as a system. The system may include afirst WLAN device configured to transmit, from the first WLAN device toa second WLAN device via a wireless channel, a first packet thatincludes a plurality of portions modulated using a correspondingplurality of MCS options. The plurality of portions may include at leasta first portion is modulated using a first MCS and a second portion ismodulated using a second MCS. The system may include the second WLANdevice configured to receive the first packet. The second WLAN devicemay be configured to determine one or more first quality metrics basedon the first portion of the first packet. The second WLAN device may beconfigured to determine one or more second quality metrics based on thesecond portion of the first packet. The second WLAN device may beconfigured to determine a selected MCS for the first WLAN device to usefor modulating a subsequent packet to the second WLAN device via thewireless channel. The selected MCS may be based on the one or more firstquality metrics and the one or more second quality metrics. The secondWLAN device may be configured to transmit a feedback message to thefirst WLAN device, the feedback message including a field populated withthe selected MCS. The system may include the first WLAN deviceconfigured to receive the feedback message and transmit the subsequentpacket using the selected MCS.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as an apparatus. The apparatus may includea modem and at least one processor communicatively coupled with the atleast one modem. The processor, in conjunction with the modem, may beconfigured to perform any one of the above-mentioned methods or featuresdescribed herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as a computer-readable medium havingstored therein instructions which, when executed by a processor, causesthe processor to perform any one of the above-mentioned methods orfeatures described herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented as a system having means for implementingany one of the above-mentioned methods or features described herein.

As used herein, a phrase referring to “at least one of” or “one or moreof” a list of items refers to any combination of those items, includingsingle members. For example, “at least one of: a, b, or c” is intendedto cover the possibilities of: a only, b only, c only, a combination ofa and b, a combination of a and c, a combination of b and c, and acombination of a and b and c.

The various illustrative components, logic, logical blocks, modules,circuits, operations and algorithm processes described in connectionwith the implementations disclosed herein may be implemented aselectronic hardware, firmware, software, or combinations of hardware,firmware or software, including the structures disclosed in thisspecification and the structural equivalents thereof. Theinterchangeability of hardware, firmware and software has been describedgenerally, in terms of functionality, and illustrated in the variousillustrative components, blocks, modules, circuits and processesdescribed above. Whether such functionality is implemented in hardware,firmware or software depends upon the particular application and designconstraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative components, logics, logical blocks, modules and circuitsdescribed in connection with the aspects disclosed herein may beimplemented or performed with a general purpose single- or multi-chipprocessor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device (PLD), discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A general-purpose processormay be a microprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, for example, a combination of aDSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes, operationsand methods may be performed by circuitry that is specific to a givenfunction.

As described above, in some aspects implementations of the subjectmatter described in this specification can be implemented as software.For example, various functions of components disclosed herein, orvarious blocks or steps of a method, operation, process or algorithmdisclosed herein can be implemented as one or more modules of one ormore computer programs. Such computer programs can includenon-transitory processor- or computer-executable instructions encoded onone or more tangible processor- or computer-readable storage media forexecution by, or to control the operation of, data processing apparatusincluding the components of the devices described herein. By way ofexample, and not limitation, such storage media may include RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that may be used tostore program code in the form of instructions or data structures.Combinations of the above should also be included within the scope ofstorage media.

Various modifications to the implementations described in thisdisclosure may be readily apparent to persons having ordinary skill inthe art, and the generic principles defined herein may be applied toother implementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

Additionally, various features that are described in this specificationin the context of separate implementations also can be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation also can beimplemented in multiple implementations separately or in any suitablesubcombination. As such, although features may be described above asacting in particular combinations, and even initially claimed as such,one or more features from a claimed combination can in some cases beexcised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one or moreexample processes in the form of a flowchart or flow diagram. However,other operations that are not depicted can be incorporated in theexample processes that are schematically illustrated. For example, oneor more additional operations can be performed before, after,simultaneously, or between any of the illustrated operations. In somecircumstances, multitasking and parallel processing may be advantageous.Moreover, the separation of various system components in theimplementations described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts. Additionally, other implementations are within the scope ofthe following claims. In some cases, the actions recited in the claimscan be performed in a different order and still achieve desirableresults.

What is claimed is:
 1. An apparatus of a first wireless device, comprising: one or more memories storing processor-executable code; and one or more processors coupled with the one or more memories and individually or collectively operable to execute the code to cause the first wireless device to: transmit, to a second wireless device, a first packet that includes a plurality of link adaptation test portions generated using a plurality of transmission rate options; receive, from the second wireless device, feedback information based at least in part on the first packet; and transmit, to the second wireless device and based at least in part on the feedback information, a subsequent packet using a first transmission rate option of the plurality of transmission rate options.
 2. The apparatus of claim 1, wherein the plurality of link adaptation test portions including a first portion modulated using a first modulation and coding scheme (MCS) and a second portion modulated using a second MCS.
 3. The apparatus of claim 1, wherein the first packet has a format based at least in part on a null data packet (NDP) defined for a wireless local area network (WLAN) associated with the first wireless device.
 4. The apparatus of claim 1, wherein the first packet includes an indication to cause the second wireless device to receive the plurality of link adaptation test portions using the plurality of transmission rate options and provide the feedback information based at least in part on the plurality of link adaptation test portions.
 5. The apparatus of claim 1, wherein the first packet is a dedicated link adaptation test packet having a format specified by a link adaptation protocol.
 6. The apparatus of claim 1, wherein the first packet further comprises upper layer data for the second wireless device.
 7. The apparatus of claim 6, wherein the upper layer data is included in a separate portion of the first packet that is different from the plurality of link adaptation test portions.
 8. The apparatus of claim 1, wherein the plurality of link adaptation test portions includes a first portion that is modulated in a first set of tones of an orthogonal frequency division multiplexed (OFDM) symbol and a second portion that is modulated in a second set of tones of the OFDM symbol.
 9. The apparatus of claim 1, wherein the plurality of link adaptation test portions includes a first portion and a second portion of the first packet, the first portion and the second portion being modulated in different orthogonal frequency division multiplexed (OFDM) symbols associated with the first packet.
 10. The apparatus of claim 9, wherein the first packet includes a series of OFDM symbols, each OFDM symbol being modulated using a different transmission rate option of the plurality of transmission rate options.
 11. The apparatus of claim 1, wherein the feedback information indicates the first transmission rate option selected by the second wireless device.
 12. The apparatus of claim 1, wherein the feedback information indicates one or more link quality metrics related to the plurality of link adaptation test portions, and the first transmission rate option is based at least in part on the one or more link quality metrics.
 13. The apparatus of claim 12, wherein the one or more link quality metrics include at least one member selected from a group consisting of: a signal to noise ratio (SNR), a signal to interference plus noise ratio (SINR), or an error vector magnitude (EVM).
 14. The apparatus of claim 1, wherein: to receive the feedback information, the one or more processors are individually or collectively further operable to execute the code to cause the first wireless device to receive an acknowledgement (ACK) message in response to the first packet; and the ACK message includes a field populated with the feedback information.
 15. The apparatus of claim 1, wherein: the first packet is a request to send (RTS) packet; to receive the feedback information, the one or more processors are individually or collectively further operable to execute the code to cause the first wireless device to receive a clear to send (CTS) message in response to the RTS packet; and the CTS message includes a field populated with the feedback information.
 16. The apparatus of claim 1, wherein: each of the plurality of link adaptation test portions is modulated using a different modulation and coding scheme (MCS); the feedback information includes a log likelihood ratio (LLR) metric indicative of a decoding success rate for each of the plurality of link adaptation test portions; and the one or more processors are individually or collectively further operable to execute the code to cause the first wireless device to select a first MCS associated with a link adaptation test portion having a highest throughput and for which a corresponding LLR metric is above a threshold.
 17. An apparatus of a second wireless device, comprising: one or more memories storing processor-executable code; and one or more processors coupled with the one or more memories and individually or collectively operable to execute the code to cause the second wireless device to: receive, from a first wireless device via a wireless channel, a first packet that includes a plurality of link adaptation test portions generated using a plurality of transmission rate options; transmit, to the first wireless device, feedback information based at least in part on the plurality of link adaptation test portions; and receive, from the first wireless device via the wireless channel and based at least in part on the feedback information, a subsequent packet transmitted using a first transmission rate option of the plurality of transmission rate options.
 18. The apparatus of claim 17, wherein the plurality of link adaptation test portions includes a first portion modulated using a first modulation and coding scheme (MCS) and a second portion modulated using a second MCS.
 19. The apparatus of claim 17, wherein the one or more processors are individually or collectively further operable to execute the code to cause the first wireless device to: select the first transmission rate option based at least in part on the plurality of link adaptation test portions.
 20. A method for wireless communication at a first wireless device, comprising: transmitting, to a second wireless device via a wireless channel, a first packet that includes a plurality of link adaptation test portions generated using a plurality of transmission rate options; receiving, from the second wireless device, feedback information based at least in part on the plurality of link adaptation test portions; and transmitting, to the second wireless device via the wireless channel and based at least in part on the feedback information, a subsequent packet using a first transmission rate option of the plurality of transmission rate options. 